Fig. 4. Biocompatibility assessment of a PEG₅₇-PHPMA₆₅ worm gel. (A) Schematic representation of the direct contact and indirect contact (ThinCert® inserts) set-ups employed to assess the toxicity of PEG₅₇-PHPMA₆₅ in the presence of human dermal fibroblast (HDF) cells. (B) Cell viability was evaluated by direct-contact cell monolayers and also via an indirect assay using ThinCert® inserts. Normalized HDF metabolic activity data obtained for triplicate experiments via MTT assays after exposure to the PEG₅₇-PHPMA₆₅ worm gel at a copolymer concentration of 8%, 10% or 12% w/w. Control experiments were performed to assess the metabolic activity of HDF cells in the absence of any PEG₅₇-PHPMA₆₅ copolymer. (C) Representative fluorescence microscopy images recorded for hPSC colonies after their immersion in a 12% w/w PEG₅₇-PHPMA₆₅ worm gel dispersed in Nutristem for either 2 or 7 days at 37 °C. Cell-permeable SYTO 9 (green fluorescent nucleic acid stain) and cell-impermeable propidium iodide (red fluorescent nucleic acid stain) were used for live/dead staining, respectively.